The present invention relates to a failure restoration system that performs routing to an alternate path across a network for partially releasing a connection setup in a main path which has encountered a failure by means of previously determining the alternate path. More specifically, the present invention relates to a failure restoration system having a routing function that calls to the destination via an alternate path if there is a failure on the main path, with as few links or nodes on the main path as possible avoided to be used. Failure restoration systems of this type are suitable for large-scale hierarchical networks such as asynchronous transfer mode (ATM) networks.
Failure restoration systems with an alternate path selection unit are well known in the art. Conventional alternate path selection units are either a centralized control type or a flooding type. Centralized control type alternate path selection units have a network management system or systems that discovers topology for an entire network. The alternate path is determined by the centralized control. The network management system in the centralized control type alternate path selection unit queries for link information associated with individual nodes to discover the topology for the entire network. The network management system previously computes routes, i.e., a main path and associated alternate paths for all combinations of nodes based on the topology information.
For the flooding type alternate path selection units, the nodes in the network dynamically and autonomously search the alternate path and set up a connection. Japanese Patent Laid-Open No. 5-114910 discloses an example of a flooding type alternate path selection unit. The alternate path selection unit carries out flooding among nodes In the same network. More specifically, the alternate path selection unit first attempts to find routes to reachable addresses with types of greatest precedence by means of distributing a control message among all nodes in the same network. A node considers a connection through which the control message reaches a destination node as the alternate path.
However, the conventional alternate path selection units have the disadvantage of not being applicable to a large-scale network. Implementing the centralized control type alternate path selection unit in a large-scale network increases a load on the unit for computing the routes. When the flooding type alternate path selection unit is implemented in a large-scale network, the control message for finding a route is distributed among all nodes in the network. Traffic becomes larger over the network for the control packet in proportion to the increase of the network scale. Thus, both the centralized control and the flooding types of alternate path selection units are not suitable for the large-scale network.